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KVM: nSVM: Save/load CET Shadow Stack state to/from vmcb12/vmcb02

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Transfer the three CET Shadow Stack VMCB fields (S_CET, ISST_ADDR, and
SSP) on VMRUN, #VMEXIT, and loading nested state (saving nested state
simply copies the entire save area).  SVM doesn't provide a way to
disallow L1 from enabling Shadow Stacks for L2, i.e. KVM *must* provide
nested support before advertising SHSTK to userspace.

Link: https://lore.kernel.org/r/20250919223258.1604852-37-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-09-19 15:32:43 -07:00
parent 48b2ec0d54
commit c5ba494585
1 changed files with 20 additions and 0 deletions
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20
arch/x86/kvm/svm/nested.c
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@ -636,6 +636,14 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
vmcb_mark_dirty(vmcb02, VMCB_DT);
}
if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) &&
(unlikely(new_vmcb12 || vmcb_is_dirty(vmcb12, VMCB_CET)))) {
vmcb02->save.s_cet = vmcb12->save.s_cet;
vmcb02->save.isst_addr = vmcb12->save.isst_addr;
vmcb02->save.ssp = vmcb12->save.ssp;
vmcb_mark_dirty(vmcb02, VMCB_CET);
}
kvm_set_rflags(vcpu, vmcb12->save.rflags | X86_EFLAGS_FIXED);
svm_set_efer(vcpu, svm->nested.save.efer);
@ -1044,6 +1052,12 @@ void svm_copy_vmrun_state(struct vmcb_save_area *to_save,
to_save->rsp = from_save->rsp;
to_save->rip = from_save->rip;
to_save->cpl = 0;
if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
to_save->s_cet = from_save->s_cet;
to_save->isst_addr = from_save->isst_addr;
to_save->ssp = from_save->ssp;
}
}
void svm_copy_vmloadsave_state(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
@ -1111,6 +1125,12 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
vmcb12->save.dr6 = svm->vcpu.arch.dr6;
vmcb12->save.cpl = vmcb02->save.cpl;
if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK)) {
vmcb12->save.s_cet = vmcb02->save.s_cet;
vmcb12->save.isst_addr = vmcb02->save.isst_addr;
vmcb12->save.ssp = vmcb02->save.ssp;
}
vmcb12->control.int_state = vmcb02->control.int_state;
vmcb12->control.exit_code = vmcb02->control.exit_code;
vmcb12->control.exit_code_hi = vmcb02->control.exit_code_hi;